The present invention relates to a combustor liner for a gas turbine for flowing hot gases of combustion and particularly relates to apparatus and methods for enhancing heat transfer from the combustor liner to a backside cooling medium.
Various techniques have been devised to maintain the temperature of gas turbine components below critical levels. For example, a coolant medium such as coolant air from the compressor of the turbine is often directed to a component along one or more component surfaces. Such flow is understood in the art as backside flow where the cooling medium is directed at a surface of the component not directly exposed to high temperatures such as the hot gases of combustion. One such component of the gas turbine is the combustor liner. It will be appreciated that the combustor liner confines the hot gases of combustion for flow along the combustor to a transition body for flow into the turbine section of the gas turbine. Combustor liners typically have ribs projecting generally radially outwardly of the liner and extending into an annulus which receives the coolant air flow on the coolant side of the liner. The metal surface of the combustor liner in the space between the ribs is normally smooth.
Combustor liners are a critical component in the combustion system for the gas turbine. However, the average life of a combustor liner is considerably less than desirable and can be less than, for example, 400 hours of operation. Accordingly, there is a need for providing a method for extending the life of the combustor liner by improving the heat transfer performance of the combustor liner as well as to provide a combustor liner having enhanced heat transfer.
In accordance with a preferred embodiment of the present invention, there is provided methods for extending the life of the combustor liner by providing enhanced heat transfer on the cooling side of the liner. In an exemplary embodiment of the present invention, the backside of the combustor liner is provided with a plurality of cooling bumps disposed along the smooth surface areas between the combustor liner ribs, on the ribs or along both surfaces, i.e., between the ribs and on the ribs. The bumps are applied in a coating of metallic powder in intimate contact with the backside surface of the combustor liner. It is believed that the enhanced heat transfer from the coated backside of the liner to the cooling medium is a result of the increased surface area afforded by the metallic bumps.
In a preferred embodiment according to the present invention, there is provided a method of enhancing heat transfer between one surface of a combustor liner for a gas turbine and a cooling medium along the one surface wherein a second surface of the liner opposite the one surface is exposed to hot gases of combustion comprising the step of applying a coating on the one surface of the combustor liner to form an overlying coated surface having a coated surface area in excess of a surface area of the one surface uncoated to afford enhanced heat transfer between the one coated surface of the combustor liner and the cooling medium relative to heat transfer between the one surface of the combustor liner and the cooling medium without applying the coating.
In a further preferred embodiment according to the present invention, there is provided a method of enhancing heat transfer between one surface of a combustor liner for a gas turbine and a cooling medium along the one surface wherein a second surface of the liner opposite the one surface is exposed to hot gases of combustion, the combustor liner including at least a pair of generally annular ribs spaced from one another and projecting in a direction away from the second surface, the ribs defining a generally annular and generally smooth area therebetween comprising the steps of providing a brazing sheet having cooling enhancement material and fusing the brazing sheet along the one surface to one of the pair of ribs and the annular smooth area between the ribs such that the cooling enhancement material is bonded thereto.
In a further preferred embodiment according to the present invention, there is provided a combustor liner having a cooling surface and an opposite surface for exposure to a high temperature fluid medium comprising a coating overlying the cooling surface forming a coated surface having a coated surface area in excess of the surface area of the cooling surface uncoated to afford enhanced heat transfer from the combustor liner to a cooling medium along the coated surface relative to the heat transfer from the combustor liner to the cooling medium without the coating.